a. Field of Invention
This invention pertains to an implantable pacemaker and more particularly to a pacemaker constructed and arranged to recognize the imminent onset of atrial fibrillation and to automatically take steps necessary for the prevention thereof. The invention further pertains to a method of detecting and preventing atrial fibrillation within an implantable pacemaker.
b. Description of the Prior Art
Since ventricular tachyarrhythmia can have grave and potentially lethal consequences, the primary concern for clinicians until recently has been the detection and reversion of this undesirable condition. While many pacemakers were also capable of detecting atrial fibrillation, this latter condition was believed to be relatively benign, if unpleasant to the patient. Accordingly, atrial fibrillation was either ignored, or treated in a palliative manner.
However, since present pacemakers are capable of treating ventricular arrhythmia rather well, much attention has turned toward the detection and treatment of atrial fibrillation (AF). There are several reasons why it is thought to be important to control atrial fibrillation. First, atrial fibrillation is associated with the loss of AV synchrony and therefore can result in irregular heart rate and a hemodynamically inefficient cardiac operation. Atrial fibrillation has also been associated with other problems such as dyspnea, fatigue, vertigo, angina pectoris, and palpitations. These conditions lead to a patient losing his ability to enjoy life and to function normally, and may limit his capability to perform work and earn a living. An especially dire consequence of atrial fibrillation is stroke which is caused by an embolism originating because of blood pooling and clotting in the left atrium.
Recent studies have shown in fact that atrial fibrillation occurs in 0.3-0.4% of the general population. Moreover, the incidence of atrial fibrillation increases with age, so that it may reach 2-4% by the age of 60, and 8-11% after the age of 75 years. However until now, the only way for pacemakers to handle atrial fibrillation, if at all, was to mode switch from dual-chamber to ventricular pacing after atrial fibrillation was detected. However, this approach requires that atrial fibrillation occur in the first place. Once atrial fibrillation sets in, its undesirable effects will be felt by the patient, and provide unnecessary stress to the heart, at least until it is reverted. Moreover, once atrial fibrillation sets in, it must be reverted relatively quickly, before it can cause the formation of emboli or other complications. Also, it has been shown that the longer a subject remains in atrial fibrillation, the more likely they are to remain in atrial fibrillation and have repeated episodes.